The invention relates to a gas discharge lamp and to its production.
In particular, the invention addresses a gas discharge lamp which is designed for dielectrically impeded discharges, in the case of which, therefore, at least the electrode(s) of one polarity is(are) separated by a dielectric layer from the discharge volume in the discharge vessel of the lamp (dielectrically impeded electrode).
The technology of gas discharge lamps, in particular of gas discharge lamps for dielectrically impeded discharges and, in turn, particularly of flat radiator gas discharge lamps, is presupposed here as prior art. In addition, reference is made as an example to the prior German Patent Application 197 11 890.9 from the same applicant, the disclosure content of which with regard to the lamp technology of flat radiator gas discharge lamps for dielectrically impeded discharges is hereby incorporated by reference.
Moreover, the invention also addresses linear discharge lamps, in particular for dielectrically impeded discharges. Reference is made in this connection to WO98/49712, the disclosure content of which with regard to the lamp technology of linear discharge lamps for dielectrically impeded discharges is hereby incorporated by reference. In the said document, a linear aperture discharge lamp with at least one internal strip-shaped electrode is disclosed. An end of the tubular discharge vessel of the lamp is closed in a gas-tight fashion by a stopper which is fused by means of glass solder to a part of the inner wall of the discharge vessel. The strip-shaped inner electrode is guided to the outside through the glass solder as a supply lead. It is disadvantageous that a glass solder layer is required between the stopper and vessel wall as gas-tight connecting means.
It is an object of the present invention to provide a gas discharge lamp whose discharge vessel can be closed in a gastight fashion relatively simply.
This object is achieved according to the invention by means of a gas discharge lamp having a discharge vessel and characterized in that the discharge vessel has at least one closure element which is fitted into a discharge vessel opening and fused and thereby closes the discharge vessel opening in a gas-tight fashion.
The basic idea of the invention consists in closing one or more openings in a discharge vessel of a discharge lamp by fusing a closure element fitted into the or each discharge vessel opening. It is possible in this way to dispense with an additional connecting means, for example a glass solder layer as in the prior art, between the closure element and the wall of the discharge vessel opening.
As a result of heating, the softening of the material of the closure element leads to a firm connection and, if appropriate, to matching of shape to the wall of the discharge vessel opening. In general terms, the term of fusing does not necessarily mean a transition into a liquid phase in the actual meaning of the word. Rather, it also conveys an adequate softening which firstly leads to adequate adhesion of the softened material to the vessel wall directly adjacent to the discharge vessel opening and, if required, to matching of the shape thereto. Typically, a viscosity of the closure element of the order of magnitude of 106 dPaxc2x7s (decipascal seconds) or less is aimed at in fusing.
In order when fusing the closure element not to impair the lamp itself, that is to say in particular the discharge vessel, possibly joined from a plurality of parts, the electrodes, if appropriate functional layers such as dielectric barriers, fluorescent materials etc., the material of the closure element is selected such that its softening temperature is below that of the remaining materials used, in particular for the discharge vessel. In particular, the softening temperature of the closure element is relatively low, such that typical temperatures for the fusing are in the region of between approximately 350xc2x0 C. and 600xc2x0 C., for example 400xc2x0 C. Firstly, the outgasings, occurring at relatively high temperatures, from the materials of the discharge vessel can thereby be suppressed or at least kept relatively slight. Furthermore, the thermal loading of the discharge vessel becomes relatively slight, as a result of which mechanical damage owing to strains or thermal changes in the material can be virtually avoided. Typically, at the fusing temperature the viscosity of the closure element is at least two, and more preferably, at least three powers of ten lower than that of the discharge vessel, with a substantially higher softening temperature, 520xc2x0 C. in the example.
Each closure element is a prefabricated semi-finished product, for example a moulded part made from sintered glass, for example lead borosilicate (Pbxe2x80x94Sixe2x80x94Bxe2x80x94O), bismuth borosilicate glass (Bixe2x80x94Sixe2x80x94Bxe2x80x94O), zinc borosilicate glass (Znxe2x80x94Sixe2x80x94Bxe2x80x94O) zinc bismuth borosilicate glass (Znxe2x80x94Bixe2x80x94Sixe2x80x94Bxe2x80x94O) or phosphate glass (SnOxe2x80x94ZnOxe2x80x94P2O5). The discharge vessel consists, by contrast, of a glass usual for this purpose, such as soda-lime silicate glass.
Such an opening closed according to the invention by fusing a closure element can be a filling opening for evacuating and filling which must be closed after the filling. In this case, the closure element can take the form, for example, of a stopper which is inserted after the filling into the filling opening and subsequently fused and thereafter closes the filling opening in a gas-tight fashion. However, a sleeve with a thickened edge, that is to say a type of collar with a bore which serves as the actual filling opening here is also suitable as closure element. This variant has the advantage that the closure element can already be inserted into the opening of the discharge vessel before the filling. After the filling, the closure element need only further be fused, and thereby the opening be closed in a gas-tight fashion.
Moreover, however, the opening can also be one through which, for example, an electrical lead-through is laid and which is to be closed tightly, the intention being to seal the lead-through. It is favourable in this case, as well, to provide the closure element that is to be fused as a thickened edge of the opening. Upon softening, the glass can then close the opening uniformly from all sides of the opening. If the opening is a filling opening, the diameter of the opening can be 1-5 mm, for example.
As already mentioned at the beginning, the invention preferably addresses flat radiator discharge vessels. These can be mounted on a base plate and a front plate as well as a frame connecting the two plates. A favourable arrangement of a filling opening can be situated in the frame in this case, because the emission of light is thereby impaired to a particularly slight extent. This also holds, in particular, for electrical lead-through. However, arrangements in the base plate or in the top plate are also possible, skilful accommodation in an edge region being preferable, in order not to disturb the emission of light and the course of the discharge electrodes.
Linear discharge lamps are also less affected by the problems of the specific favourable arrangement of a filling opening, since a discharge tube firstly necessarily has at its two ends one opening each which is suitable for filling, and these have to be closed, for example, by the closure elements according to the invention.
Heating for the purpose of fusing the closure element can be realized in any case by thermal radiation, in a furnace or by means of an IR radiator, for example, or by a flame.
With regard to the device suitable for such method steps, the invention further addresses the carrying out of the method in a vacuum furnace for the purpose of evacuating and filling in simultaneous conjunction with a temperature which is raised under control.
The invention is explained below in more concrete terms with the aid of a plurality of exemplary embodiments, it being possible for the features disclosed in this case also to be essential to the invention individually or in combinations other than those illustrated.